1. Field of the Invention
This invention relates generally to drum type washing machines, and more particularly to such a drum type washing machine including an electric motor directly rotating a rotating tub.
2. Description of the Prior Art
FIG. 14 illustrates one of conventional drum type washing machines. The shown drum type washing machine comprises an outer cabinet 1 and a water tub 2 elastically supported by a plurality of suspension mechanisms 3 in the cabinet. A drum-shaped rotating tub 4 is provided for rotation in the water tub 2. A bearing housing 6 is mounted on a rear wall of the water housing 2. The rotating tub 4 has a shaft 5 extending rearward from a rear thereof. The shaft 5 is supported on bearings 7 and 8 held in the bearing housing 6. The shaft 5 has a rear end to which a driven pulley 9 is mounted. A motor support 10 is mounted on a lower portion of the water tub 2. An electric motor 11 is supported by the motor support 10. The motor 11 includes a rotational shaft 12 on which a driving pulley 13 is mounted. A transmission belt 14 extends between the driving and driven pulleys 13 and 9.
In the above-described construction, torque developed by the motor 11 is transmitted via the shaft 12, driving pulley 13, belt 14 and driven pulley 9 to the shaft 5 so that the rotating tub 4 is rotated. However, a belt transmission mechanism including the driving and driven pulleys 13 and 9 and the belt 14 complicates the construction of the washing machine and accordingly increases the manufacturing cost. Furthermore, each of the pulleys 13 and 9 and the belt 14 produces oscillation or vibration in the transmission of motor torque. In particular, high-speed rotation of the motor 11 causes the belt 14 to slip, thereby swinging the belt. This increases the vibration produced by the belt transmission mechanism such that a loud noise is produced.
To solve the above-described problem, the prior art has provided a drum type washing machine as shown in FIG. 15. The drum type washing machine shown in FIG. 15 comprises a water tub 2 and an electric motor 21 provided on a rear wall of the water tub 2. More specifically, a mounting member 24 is fixed on the rear wall of the water tub 2 so as to cover a bearing housing 6. The motor 21 includes a stator 23 fixed to the mounting member 24. The motor 21 also includes a rotor 22 connected to a rear end of a shaft 5 of the rotating tub. Japanese Patent Application Publication No. 9-182369 (1997) also discloses a drum type washing machine having the same construction as described above.
Torque developed by the motor 21 is directly transmitted to the shaft 5 and accordingly to the rotating tub 4 without a belt transmission mechanism in the aforesaid drum type washing machine. As a result, the construction of the driving mechanism for the rotating tub 4 is simplified and the manufacturing cost can be reduced accordingly. Furthermore, the vibration and noise can be reduced since no belt transmission mechanism is required.
Generally speaking, when a center of a stator and a center of rotation of a rotor of an electric motor are displaced relative to each other, an air gap defined between the stator and rotor is varied depending upon a rotation angle. This reduces the accuracy of the motor and produces vibration and noise. Accordingly, the center of the stator and the center of rotation of the rotor need to agree with each other with the greatest circumspection. The motor 11 as an end product is mounted on the lower portion of the water tub 2 in the conventional drum type washing machine. Accordingly, the center of the stator and the center of rotation of the rotor need not be aligned with each other regarding the motor 11.
On the other hand, the motor 21 includes a combination of the stator 23 fixed to the mounting member 24 and the rotor 22 fixed to the rear end of the shaft 5. More specifically, the center of the stator 23 and the center of rotation of the rotor 22 need to be aligned with each other. Thus, the motor 21 needs to be mounted with the greater circumspection in the aforesaid direct-drive drum type washing machine than in the aforesaid drum type washing machine with the belt transmission mechanism. Further, laundry sometimes tends to be one-sided during a dehydrating operation regarding the aforesaid drum type washing machine with the belt transmission mechanism. When the laundry becomes one-sided, the magnitude of centrifugal force acting on a portion of the rotating tub 5 differs from the magnitude of centrifugal force acting on the other portion of the rotating tub. For example, when laundry in the rotating tub 4 is one-sided at an area A shown by the two-dot chain line in FIG. 14, a large centrifugal force F1 is applied to the area A, the bearings 7 and 8 in the bearing housing 6 are subjected to loads F2 and F3 respectively.
Since bellows connect an opening side of the water tub to the outer cabinet in each of the aforesaid drum type washing machine, a supporting structure for the water tub tends to become more rigid than the one of an automatic washing machine of the vertical axis type. When a part of the rotating tub is subjected to a large centrifugal force F1 during the dehydrating operation, the loads F2 and F3 acting on the respective bearings 7 and 8 are increased such that the bearing housing 6 and parts around the bearing housing would be deformed. In the drum type washing machine shown in FIG. 14, the motor 11 is not almost affected by the loads F2 and F3 both acting on the bearing housing 6 since the motor is mounted on the lower portion of the water tub 2. More specifically, the motor 11 is subjected to no large force other than the tension F4 of the belt 14.
On the other hand, the stator 23 is fixed on the mounting member 24 surrounding the bearing housing 6 in the drum type washing machine shown in FIG. 15. Accordingly, the stator 23 is easy to be affected by the loads F2 and F3. The positional relation between the rotor 22 and the stator 23 changes when the bearing housing 6 and the mounting member 24 are deformed by the loads F2 and F3. As a result, the center of the stator 23 and the center of rotation of the rotor 22 are displaced relative to each other.
Furthermore, in the drum type washing machines, a washing/dehydrating capacity and a rotational speed in the dehydrating operation differ from one type to another. In the case of a drum type washing machine having a large washing/dehydrating capacity, the size of the rotating tub 4 is increased and a larger amount of laundry is accommodated in the rotating tub. Thus, the washing machine of the large capacity type requires a larger drive torque than that of the small capacity type. Further, the washing machine with a high rotational speed for the dehydrating operation requires a higher durability of the shaft 5 than that with a low rotational speed for the dehydrating operation. Accordingly, the diameter of the shaft 5 tends to be increased.
In view of the above-described problem, the construction of the connection between the shaft 5 and the driven pulley 9 or between the shaft 5 and the rotor 22 needs to be changed according to the washing capacity, the dehydrating capacity or the rotational speed in the dehydrating operation. The construction of the connection between the shaft 5 and the driven pulley 9 is changed in the following manner. The driven pulley 9 is die-cast from aluminum and accordingly, the construction can easily be changed by cutting a portion of the driven pulley 9 connected to the shaft 5. On the other hand, when the shaft 5 and the rotor 22 are cut so that the construction of the connection between them is changed, there is a possibility that the center of the stator 23 and the center of rotation of the rotor 22 may be displaced relative to each other. As a result, the air gap defined between the stator and rotor is varied such that the accuracy of the motor is adversely affected. Consequently, the construction of the connection between the shaft 5 and the rotor 22 cannot easily be changed in the drum type washing machine of the direct drive type.
Therefore, an object of the present invention is to provide a drum type washing machine wherein an electric motor is provided on a rear wall of the water tub for directly driving the rotating tub and the center of rotation of the rotor and the center of the stator can easily be aligned with each other.
The present invention provides a drum type washing machine comprising an outer cabinet, a water tub mounted in the outer cabinet and having a rear end plate, a generally drum-shaped rotating tub rotatably mounted in the water tub and having a rear wall, a rotating tub shaft provided on a center of the rear wall of the rotating tub and having a rear end projecting rearward to be located in the rear of the rear end plate of the water tub, an electric motor provided for rotating the rotating tub via the rotating tub shaft, the motor including a stator provided on the rear end plate of the water tub and a rotor connected to the rear end of the rotating tub shaft, a bearing housing provided on the rear end plate of the water tub and having a bearing element supporting the rotating tub shaft so that the rotating tub shaft is rotatable, and an aligning structure for aligning a center of rotation of the rotor and a center of the stator.
According to the above-described construction, the center of rotation of the rotor and the center of the stator can reliably be aligned with each other even though the stator is provided on the rear end plate of the water tub and the rotor is connected to the rear end of the rotating tub shaft. Consequently, the rotor and the stator can be mounted easily.
In a preferred form, the aligning structure includes a positioner formed integrally on an outer periphery of the bearing housing for radially positioning the stator. The position of the stator relative to the bearing housing can be prevented from being changed even when the bearing housing is subjected to load such that the bearing housing and the parts around the bearing housing are deformed. In other words, the position of the stator relative to the rotating tub shaft supported on the bearing housing and accordingly the rotor can be prevented from being changed. Consequently, the center of rotation of the rotor and the center of the stator are prevented from being deviated from each other and the dimension of the air gap between the stator and the rotator can be prevented from being deviated.
In another preferred form, the stator is fixed to the bearing housing. Since the positioner and the stator are mounted on the same member, the stator can be positioned accurately. Furthermore, the positioner preferably includes an abutting portion abutting against the stator radially outward, and the abutting portion has an axial dimension equal to or larger than an axial dimension of the stator. The abutting portion of the positioner can be caused to abut against the stator even when the axial position of the stator is slightly shifted.
In further another preferred form, the motor is of an outer rotor type, and the stator has such a generally annular shape as to surround the bearing housing. In this case, the stator has an inner circumferential face formed with an inwardly extending protrusion, and the positioner is constructed so as to abut against the protrusion. Alternatively, the positioner is formed into such a generally convex shape as to outwardly extend such that the protrusion abuts against the inner circumferential face of the stator. In each construction, the stator can easily be radially positioned.
In further another preferred form, the drum type washing machine further comprises a reinforcement for reinforcing the rear end plate of the water tub. In this case, the bearing housing is formed integrally with the reinforcement, and the positioner is disposed on the outer periphery of the bearing housing so as to align with the reinforcement. Consequently, the strength of the positioner can be improved.
In further another preferred form, the aligning structure includes a connecting member connecting the rotor and the rotating tub shaft to each other. Consequently, the construction of the connection between the rotor and the rotating tub shaft can be changed only by changing the construction of the connecting member. Consequently, the center of rotation of the rotor and the center of the stator can be prevented from being deviated from each other. The connecting member preferably includes a rotor connecting member mounted to the rotor and a shaft connecting member mounted to the rotating tub shaft. In this case, the rotor connecting member is formed on the rotor by an insert molding method, and the shaft connecting member is press fitted in the rotating tub shaft. Even when the rotor and the rotating tub shaft are connected by the rotor and shaft connecting members, a decrease in the strength of each connection can be prevented.